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Mark's Hexapod

PostPosted: Thu Dec 23, 2010 2:18 pm
by Mark
Hello everyone
My name is Mark.
My major is Embedded systems and my minor is Robotics.

I started my hexapod project in 2008 after seeing a youtube video of IC hexapod. Because I didn’t knew anything about hexapods or robotics in general it took me a while to actually started building one. Especially because I found out that making your own hexapod from scratch isn’t really cheap.

I started searching for strong servo’s. Because I had no idea about the weight it would be, I chose the MG995 servo from Towerhobbies. They only cost about 7dollar on ebay and can lift up to 15kg/cm and they can operate at a voltage of 7,2V wich is nice because I also use them in my RC cars. They are cheap and strong but have some downsides. They draw a awfull lot of current and are pretty shaky. But for now it’s ok for me.

Next I designed the frame and legs. They are inspired on Matt’s B.F. Hexapod. I had never worked with AutoCad before so I had to learn it by trail and error. So after about 2 months I had all my parts ready for cutting. This was done at school because I had a friend who could do it for me and it was for free.

The next thing I did was thinking about a way to control all the servo’s. I wanted to control all the servo’s by an i2c bus. I designed a PCB in the shape of a servo. On this PCB there is an Atmega8 whice converts the i2c data in three PWM signals.

At the moment I’m busy with a lot of things:
- Designing the main PCB whice will sends data to the legs
- Thinking about the power source.
- I'm doing some test with a webserver from tuxgraphics so I can control my hexapod though my home network so day.
- Making a website were I can show my progress and other projects concerning my rc cars.

Here are some pictures:

I know it doesn't look as awesome as some others but this is my first hexapod an I am on a budget.
But of course comments and questions are welcom.

Re: Mark's Hexapod

PostPosted: Tue Dec 28, 2010 7:46 pm
by Matt Denton
Hi Mark,

Welcome to the forum, your hex looks great! I look forward to seeing you progress with your design!

My early hexapods used a similar 3 channel servo controller, one for each leg, however, I sent data to them via a simple one way TTL serial link,

Re: Mark's Hexapod

PostPosted: Mon Jun 20, 2011 12:25 pm
by Mark
A very very short update on the project.
Because I'm busy with my graduation project I don't have much time, but I got a bit annoyed of the bad resulution of the MG995 servo's so I replaced them by MG996R.
These are just as strong only the resolution is much better and they use a bit less current.

Re: Mark's Hexapod

PostPosted: Mon Sep 26, 2011 6:56 pm
by Mark
Little update.

I'm getting rid of the Towerpro servo's.
For the coxa I will use Futaba S3003's.
I think these will be strong enough and draw less current than the Mg996R's.
I sold most of the MG996R's, and I want to replace the femur and tibia servo's with Hitec servo's
Only I don't know with one will be good enough.
If found:
- HS-325HB
- HS-311
- HS-322HD
- HS-422
- HS-77
- HS-425BB

I know the HS-645 is one of the most used servo's but that one is slightly out of my budget.
Is it worth to wait and save some money and buy the HS-645 or is it possible that I use one of the other servo's I found.
My hexapod will weigh little over 2kg.
Please let me know.

Re: Mark's Hexapod

PostPosted: Tue Sep 27, 2011 10:15 am
by Matt Denton
My advise would be to wait and buy the 645MG servos, you will have a much better experience with these!

Re: Mark's Hexapod

PostPosted: Tue Sep 27, 2011 1:54 pm
by Mark
Ok than I will wait and save some money.

Does somebody know how much current an HS-645 uses with and without load?
I'm using an 8A continous 15A burst current regulator.
Will this be enough to power 12 HS-645's and 6 S3003's?

Re: Mark's Hexapod

PostPosted: Tue Sep 27, 2011 5:09 pm
by Matt Denton
Diffucult to say how much current with and without load as it very much depends on how much load, however, I would say that the 8A contuniuous 15A peak is more than enough for your requirments. From memory I think our H01 hexapods that use 12 x HS-645MG servos and 6 x HS-225 servos will draw about 3 to 4 amps when walking depending on the gait.

Re: Mark's Hexapod

PostPosted: Tue Sep 27, 2011 7:43 pm
by Mark
Excellent .
Just the information I wanted to hear :D

Re: Mark's Hexapod

PostPosted: Sat Jun 23, 2012 4:18 pm
by Mark
A little update.

I bought 12 HS-645MG servo's (thanks Matt :D ) and fitted them in my Hex.
First tests are really positive.
Great torque, great accuracy and low current consumption.
I also bought an 32 channel servo controller on ebay.
It has a resolution of 1uS and an easy to use TTL interface on 115200kBd or 128000kBd.
The symmetrical design is what I really like and the USB interface is a big advantage over the SUB-D of the SSC-32.
Here a picture of the board:

The next think I did was a mount for the head.
it has an small SG90 servo so it can move from left to right.

This is the current state of the hex:

I'm working on the PCB(still :oops: ).
There will be one PCB in the body which holds the 6V BEC, servo controller, 5V switching regulator and some other components that controls the starting up and shutting down of the hexapod.
An other PCB in the head will control the IK, sensor data and full color display.
But I still need to figure some things out.
How do you guys connect your battery to the PCB?
Some kind of connector?
Please let me know.

Re: Mark's Hexapod

PostPosted: Sat Jun 23, 2012 6:51 pm
by Matt Denton
Hey looking good Mark! The little USB servo controller is neat, what is the control API like?

For the battery I would use an in-line connector like a tamiya battery connector or anderson 30A type.